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Re: Cassandra: Inconsistent data on reads (LOCAL_QUORUM)


Mick, sorry I think I missed your following questions:


- SPECULATIVE_RETRY='ALWAYS' 

We saw this issue a couple of times a few years ago. That's why we introduced this change. Although at that time, it was on cassandra 1.x version. 


- Topology changes:

The only change we did was that we added nodes for 2 months. But that process finished 1 month ago. Since then we've run multiple repairs on the table. Other than that no other topology changes were done. 


From: Mick Semb Wever <mick@xxxxxxxxxxxxxxxxx>
Sent: Wednesday, October 24, 2018 4:12:57 AM
To: user@xxxxxxxxxxxxxxxxxxxx
Subject: Re: Cassandra: Inconsistent data on reads (LOCAL_QUORUM)
 
[ This email has been sent from a source external to Epsilon. Please use caution when clicking links or opening attachments. ]

Ninad,

> Here's a bit more information:
>
> -Few rows in this column family can grow quite wide (> 100K columns)
>
> -But we keep seeing this behavior most frequently with rows with just 1 or two columns . The typical behavior is: Machine A adds a new row and a column. 30-60 seconds later Machine B tries to read this row. It doesn't find the row. So the application retries within 500ms. This time it finds the row.


You wrote a lot of useful info in your original post, sorry I missed
it in my first reply.
Only thing there that stands out, apart from short reads that Jeff's
already pointed out, is the use of `speculative_retry='ALWAYS'`. Has
there topology changes in your cluster recently?

Next step would be to try and repeat it with tracing.

regards,
Mick


--
Mick Semb Wever
Australia

The Last Pickle
Apache Cassandra Consulting
http://www.thelastpickle.com

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